Electrophotographic material



3,041,165 Patented June 26, 1962 3,041,165 ELECTROPHOTOGRAPHIC MATERIAL Oskar Siis, Kurt-Walter Kliipfel, Wilhelm Neugebauer,

Martha Tomanek, and Hans Behmenburg, all of Wiesbaden-Biebrich, Germany, assignors, by mesne assignments, to Kalle Aktiengesellschaft, Wiesbaden-Biebrich,

Germany, a corporation of Germany No Drawing. Filed July 2, 1957, Ser. No. 669,469 Claims priority, application Germany July 4, 1956 r 22 Claims. (Cl. 96-1) This invention relates to photographic reproduction and more particularly to electro-photographic processes, namely processes in which an electrostatic latent image is produced by utilizing the property of photoconductivity (i.e., a variable conductivity dependent on the intensity of illumination). The electrostatic latent image may be produced in a conventional exposure operation, for example by means of a lens-projected image or by contact-printing techniques, whereby a non-visible electrostatic charge pattern (the so-called electrostatic latent image) is created on a surface, in which pattern the charge density at any point is related to the'intensity of illumination obtaining at that point during the exposure. The latent image may be developedi.e., rendered visible -by means of an electroscopic powder, such as a colored synthetic resin powder, and the resulting visible image may be fixed by rendering the powder permanently adherent to a support on which the image. is desired, for example, in suitable cases by heating to soften or melt the powder particles and/ or the surface of the image support, or with volatile solvents.

In electro-photographic processes the electrostatic latent image is commonly formed onthe surface of a photo conductive insulating layer carried on a support. For example, material comprising such support and photo-conductive layer may be sensitized by applying a uniform surface charge to the free surface of the photoconductive layer. Such surface charge may be applied, for example,

a by means of a corona discharge, which charge is retained owing to the substantial insulating character, i.e., the low conductivity, of the layer when not exposed to light. On exposure as described above, the photo-conductive property of the layer causes the conductivity to increase in the illuminated areas to an extent dependent on the intensity of illumination, whereby the surface charge in the illuminated areas leaks away, leaving the charge located in the unilluminated areas. This remaining charge constitutes the aforementioned charge pattern or electrostatic latent image. 7

Electro-photographic processes have become of increasing importance in recent years, especially, for example, in connection with ofiice duplicating where, offering as they do a wholly dry copying process, they have considerable attractiveness. Much interest has been aroused and investigation made, particularly in regard to suitable materials for use as a support and as a photoconductive insulating layer adapted to such processes. A great many attempts have been made to provide such materials which fulfill modern requirements in respect to range of use, reliability, simplicity in handling, potential light sensitivity and keeping qualities.

Among photo-conductive substancesapplied hitherto, selenium has been the most notable, although many other proposals have also been made. However, none of these prior proposals has met all the necessary requirements. Such requirements have, nevertheless, now been met by the present invention.

According to preferred embodiments of the present invention, the photoconductive substances are of the general formulae in which R, and R each represents a univalent carbo nated R may comprise a naphthyl group, or a phenyl group having a nitro group as an orthoor para-substituent therein. The groups designated R may comprise a naphthyl group or a phenyl group having a methoxy group as an orthoor para-substituent therein.

The compounds covered by the above general formulae can be prepared in manner known per se. Those compounds corresponding to the general Formula I may usually be obtained by condensation of equimolecular parts of an aromatic or heterocyclic aldehyde and a primary aro matic or heterocyclic amine, the reaction components being heated in alcoholic solution with or without added alkaline condensation agents, such as piperidine, sodium carbonate solution, sodium or potassium hydroxide. A great number of them are already described in the literature; in the case of others, details concerning preparationare given below.

Those compounds which correspond to the general F ormula II are ordinarily best prepared by condensation of equimolecular parts of a compound with an active methylene group adjacent to a cyano group, (e.g. benzyl cyanamide, w-cyano-acetophenone, malonic acid dinitrile or cyano-acetic acid alkyl ester), and an amino nitroso compound of the benzene series, e.g., p-nitroso-alkyl-aniline, or p-nitroso-dialkyl-aniline, the reaction components being heated in alcoholic solution in the presence of alkaline condensation agents. The compounds corresponding to Formula II are also for the most part described in the literature. For those examples mentioned herein that are not so described the method of preparation is given here below.

Examples of specific compounds used in this invention are listed as follows:

FORMULA 1 3 FORMULA 2 H -H, LN im FORMULA 3 FORMULA 4 CH3 H CH:

C s CH3 FORMULA 5 OH, H

0Q, FORMULA 6 H I '0 zN-O-(J =NOO 0 FORMULA 7 H HzN(3=NC 0 CH U I FORMULA 8 H CH:

FORMULA 9 V H (I311! NO: CH9

FORMULA 10 FORMULA 11 i l \CHI N O:

FORMULA 12 FORMULA 1-3 FORMULA 14 4 FORMULA 1s FORMULA 16 FORMULA 17 FORMULA 23 FORMULA 24 -(F N OH: H [CH1 FORMULA 25 C-CH H FORMULA 26 FORMULA 27 FORMULA 28 FORMULA 29 FORMULA 30 (3N /om FORMULA 31 C 3 3 G C=N N CN CH:

FORMULA 32 111 OCN The following are examples of compoundscorresponding 'tothe general Formula I given above with reference being made to the above list of compounds:

Benzylidene-B-naphthylamine, corresponding to Formula 7 l; melting point 10=1102 C.

6 S-benzylidene-amino-acenaphthene, corresponding to Formula 2; melting point 6972 C. 3-benzylidene-aminmcarbazole, corresponding to Formula 3; melting point 208-209 C.

1 [4 N,N dimethylamino benzylidene] amino- 4-N,N-dimethylaminmbenzene, otherwise known as (4- N,N-dimethylamino benzylidene)-pN,N-dimethylaminoaniline, corresponding to Formula 4, melting point 221 'C., which may be prepared by boiling an ethyl alcohol solution of 14.9 g. of p N,N-dimethylamino-benzaldehyde with 13.6 g. of pN,N-dimethylamino-aniline for one hour. After the reaction mixture has cooled, the condensation product precipitates out in crystalline form and can be filtered 0E and purified by recrystallizin g from dioxane.

[4 LN dimethylamino benzylidene] {3 naphthylamine, corresponding to Formula 5, (melting point 162- 164 C.) which can be prepared by boiling an ethyl alcohol solution of 14.9 g. of p-N,N-dimethylamino-benzaldehyde with 14.3 g. of B-naphthylamine for one hour. After the reaction mixture has cooled the condensation product precipitates out of the solution in crystalline form, and can be separated by filtration, and recrystallized from 96% ethyl alcohol.

(4-nitro-benzylidene) 4 methoxy aniline, otherwise known as (4-nitro-benzylidene)-p-anisidine, correspond ing to Formula 6, melting point 139 C.

(4' amino benzylidene)-4-methoxy-aniline, otherwise known as (4-amino-benzylidene)-p-anisidine, corresponding to Formula 7, (melting point C.), which may be prepared by catalytic reduction of the compound cor responding to Formula 6 in dioxane with Raney nickel.

N,N-dimethyl-N'-(4-nitr0-ben2ylidene)-p-phenylene diamine, corresponding to Formula 8; melting point 218 C. (2'-nitro-benzylidene)-3,5-dimethyl-aniline, otherwise known as (2-nitro-benzylidene)-sym.-m-xylidene, corresponding to Formula 9; melting point C.

(2-nitro-benzylidene)-p-bromo-aniline corresponding to Formula 10; melting point 96 C.

N,N dimethyl N (2 nitro 4 cyano benzylidene)-p-phenylene-diamine, corresponding to Formula 11, (melting point 103104 C), which may be prepared by condensing 4 g. of p-nitrosodimethylaniline with 4 g. of 3-nitro-tolunitrile in 30 ml. of ethyl alcohol, by heating for a short time with 0.3 ml. or" 33% sodium hydroxide solution. After the reaction mixture has cooled the condensation product is precipitated from the solution in crystalline form; the mother liquor is filtered 011 and the precipitate is recrystallized from ethyl alcohol.

(4'-phenyl-benzylidene) -4-methoxy-aniline, otherwise known as (4-phenyl-benzylidene)-p-anisidine, correspondingto Formula 12, (melting point 182 C.) may be prepared by condensing l.8 g. of 4-diphenylaldehyde with 1.2 g. of p-anisidine in 15 ml. of ethyl alcohol, the reaction being brought about by brief heating. The reaction mixture is allowed to cool and the precipitate which has by then fallen out, is separated from the mother liquor and recrystallized from ethyl alcohol.

(4-phenyl-benzylidene)-m-chloroaniline, corresponding to Formula 13, (melting point C.), may be prepared by condensing 1.8 g. of 4-diphenylaldehyde with 1.3 g. of m-chloroaniline in 20 ml. of ethyl alcohol. The reaction mixture is heated for 30 minutes on the steam bath and the reaction product that precipitates out as the reaction mixture cools and is recrystallized from ethyl alcohol.

accrues (a-naphthobenzylidene)-u-naphthylamine, corresponding to Formula 15; melting point 117 C.

1-furfurylideneamino-2-rnethyl-5-nitro-benzene, otherwise known as (furfurylidene)-(2-methyl 5-nitro) -aniline, corresponding to Formula 16 (melting point 151 C.), which may be prepared by condensing 4.8 g. of furfural with 7.6 g. of 4-nitro-o-toluidine in 25 ml. of absolute ethyl alcohol, the reaction mixture being heated for a short time on the steam bath.

(Furfurylidene)-o-chloroaniline, corresponding to Formula 1'7 melting point 67 C.

v(Furfurylidene)-p-nitraniline, corresponding to Formula 18; melting point 140 C.

(4-N,N-dimethylamino-benzylidene -3 -amino-pyridine, corresponding to Formula 19 (melting point 86 C.), which may be prepared by condensing 1.9 g. of 3-amino pyridine with 3.0 g. of p-N,N-dimethylamino-benzaldehyde in a little ethyl alcohol, the mixture being submitted to fairly prolonged heating on the steam bath. The reaction mixture is allowed to cool and the precipitate which then forms is separated by filtration from the mother liquor and recrystallized from a benzene-petroleum ether mixture.

(4-nitro-benzylidene)-3-amino-pyridine, corresponding to Formula 20, melting point 159 C., which may be prepared as follows: 0.9 g. of 3-amino-pyridine are dissolved in 5 m1. of ethyl alcohol and the resulting solution mixed with a solution of 1.5 g. of 4-nitro-benzaldehyde in ml. of ethyl alcohol. The mixture is heated on the steam bath, and condensation takes place. The condensation product is collected by filtration and recrystallized from ethyl alcohol.

(4 N,N dimethylamine benzylidene) 6 aminoquinoline, corresponding to Formula 21 (melting point 120 C.), which may be prepared by condensing 1.4 g. of 6-amino-quinoline with 1.5 g. of 4-dimethylaminobenzaldehyde in ml. of ethyl alcohol. The reaction mixture is heated for ten minutes on the steam bath and the reaction product is crystallized out by cooling with ice.

(p-Methoxybenzylidene) 6 amino quinoline, corre sponding to Formula 22 (melting point 101), which may be prepared by condensing 1.4 g. of 6-amino-quinoline with 1.4 g. of anisaldehyde in 10 ml. of ethyl alcohol. The reaction mixture is heated on the steam bath for ten minutes and then cooled with ice, whereupon the reaction product crystallizes out.

Anthracylidene-aniline corresponding to Formula 23 (melting point 124-125 C.), which may beprepared by briefly heating an ethyl alcohol solution containing 20.6 g. of 9-anthracene-aldehyde and 9.3 g. of aniline. The condensation product precipitates out after the reaction mixture has cooled, is separated by filtration from the mother liquor and purified by recrystallization from 96% ethyl alcohol.

5- anthracylidene-amino) -acenaphthene, corresponding to Formula 24 (melting point 158-160 C.), which may be prepared by boiling an ethyl alcohol solution containing 20.6 g. of 9-anthracenealdehyde and 16.9 g. of 5- aminoacenaphthene, for one hour.

Thienylidene-B-naphthylamine corresponding to Formula 25 (melting point 103'104 C.), which can be prepared by briefiy heating an ethyl alcohol solution containing 11.2 g. of 2-thiophenaldehyde and 14.3 g. of fi-naphthylamine. The condensation product precipitates out in crystalline form after the reaction mixture has cooled. The reaction product is purified by recrystallization from 96% ethyl alcohol.

Thienylidene-a-naphthylamine, corresponding to Formula 26, (melting point 76 C.), which can be obtained by boiling an ethyl alcohol solution containing 11.2 g. of 2-thiophenaldehyde and 14.3 g. of a-naphthylamine. After the reaction mixture has cooled, the condensation product precipitates out, and can be recrystallized from 96% ethyl alcohol.

Thienylidene-amino-acenaphthene, corresponding to Formula 27, melting point 104 C., which can be obtained by boiling an ethyl alcohol solution containing 11.2 g. of Z-thiophenaldehyde and 16.9 g. of S-aminoacenaph thene.

Bis (4 N,N dirnethylamino benzylidene) p phenylene diamine, corresponding to Formula 28, (melting point 290295 C.), which can be obtained by boiling an ethyl alcohol solution containing 29.8 g. of pdimethylamino-benzaldehyde and 10.8 g. of p-phenylene diamine. After a short time the condensation product, a red crystalline substance, precipitates out from the hot solution.

N,N dimethyl N-- (2,4 dihydroxy benzylidene)- p-phenylene diamine, corresponding to Formula 29 (melting point 214-215 C.), which may be prepared by con- (lensing 13.6 g. of p-N,N-dimethylamino-aniline with 13.8 g. of 2,4-dihydroxybenzaldehyde in ethyl alcohol solution. The reaction takes place at room temperature. The precipitated reaction product is recrystallized from ethyl alcohol.

The following compounds are examples of those coming under the general Formula II given above, reference being made to the above listed formulae:

N,N dimethyl N (4-nitro-ot-cyano-benzylidene)- p-phenylene diamine, corresponding to Formula 30; melting point 175-176 C.

N,N dimethyl N (a-cyano-benzylidene)-p-phenylene diamine corresponding to Formula 31; melting point 88-90 C. v

N,N dimethyl N (benzoyl-cyano-methylene)-pphenylenediamine, corresponding to Formula 32 (melting point 129130 C.), which can be prepared by condensing 1.3 g. of w-cyanoacetophenone with 1.3 g. of pnitroso-N-dimethylaniline in 15 ml. of ethyl alcohol, to which 2 drops of 33% sodium hydroxide solution have been added, the reaction being brought about by brief heating on a steam bath.

N,N dimethyl N (dicyanomethylene) -p-phenylene diamine, corresponding to Formula 33; melting point 165 C.

N,N dimethyl N (carbethoxy-cyanomethylene)- p-phenylene-diamine, corresponding to Formula 34, melting point 9091 C.

N,N diethyl N (a-cyanobenzylidene)-p-phenylenediamine, corresponding to Formula 35; melting point C.

N methyl N (u-cyanobenzylidene)-p-phenylenediamine, corresponding to Formula 36; melting point C.

N ethyl N (a-cyanobenzylidene)-p-phenylenediamine, corresponding to Formula 37; melting point C.

N,N diethyl N (ot-cyanobenzylidene)-p-phenylenediamine corresponding to Formula 38; melting point Ethyl alcohol wherever used on pages 12 to 17 means 96% ethyl alcohol, except where otherwise stated.

The compounds to be used as provided by the invention have very good photoconductivity and are particularly suitable for the preparation of homogeneous layers which have a long shelf-life. Most of the compounds are of yellow color.

The photoconductive substances which are used according to the invention for the preparation of the photoconductive insulating layers are preferably so used in solution in organic solvents, such as, for example, benzene, acetone, methylene chloride or glycol-monomethyl-ether. Mixtures of two or more photoconductive substances may also be used in such solution as may mixtures of solvents. It is also possible to employ the photoconductive substances in association with other organic photoconductive substances.

It has further been found advantageous in preparing the photoconductive insulating layers to use the photoconductive substance or substances in association with a resin synthetic polymer or other organic colloid, for example:

Natural and synthetic resins, e.g., balsam resins, phenol ins, which includes processed natural substances such as cellulose ether, see the Kunststofitaschenbuch (Plastics Pocket Book) published by Saechtling-Zebrowski (11th edition, 1955) from page 212;

Polymers (including co-polymers) such as the polyvinyl chlorides, polyvinyl acetate, polyvinyl acetals, polyvinyl alcohols, polyvinyl ethers, polyacrylic and polymethacrylic esters, and polystyrene and isobutylene polymers;

Polycondensates, e.g., polyesters, such as phthalate resins, alkyd resins, maleic acid resins, colophony esters of mixed higher alcohols, phenol-formaldehyde resins, particularly colophony-modified phenol-formaldehyde condensates, urea-formaldehyde resins, melamine-formaldehyde condensates, aldehyde resins, ketone resins of which particular mention is to be made of AW 2 resins of the form Badische Anilinund Sodafabrik, xylene-formaldehyde resins'and polyamides;

Polyadducts, such as polyurethanes.

When the photoconductive substances are employed in association with organic colloids, the proportion of resin to photoconductive substance can be varied very greatly. The use of mixtures of approximately equal parts by weight of resin or other colloid and photoconductive substance has been found generallyadvantageous. When such mixtures of approximately equal parts by Weight of resin and photoconductive substance are used, in most cases said solutions give homogeneous transparent layers on drying that can beconsidered as solid solutions.

The support may be of any material suitable for use in electrophotographic processes as, for example, aluminum or other metal plates or foils; glass plates; paper sheets or webs, or plastic foils, especially foils made of electrically conductive resins. If paper is to be used as support for the photoconductive layer, it is preferable that it shall have been pretreated against penetration by the coating solution, for example, with methyl cel-' lulose in aqueous solution; polyvinyl alcohol in aqueous solution; a solution in acetone and methyl-ethyl-ketone of a mixed polymer of acrylic acid methyl ester and acrylonitrile; or with solutions of polyamides in aqueous alcohols. Aqueous dispersions of other substances suitable for the pretreatment of the paper surface may also be used.

Solutions of the photoconductive substances in organic solvents as described above, with or Without the added organic colloids aforementioned, can be applied to the supports in known manner (for example, by spraying, direct application, or whirl coating), and the supports thus coated, dried, so that an even photoconductive layer is formed thereon.

While the layers are, in themselves, non-light-sensitive, by applying a positive or negative electrostatic charge thereto, by means, for example, of a corona discharge, the layers are rendered light-sensitive and can be used With long-wave U.V. light of 3,600 to 4,000 A.U. in producing electrostatic latent images as described above. Very good images may be obtained by a short exposure under a master to a high-pressure lamp.

Although the layers when charged are but slightly sensitive to light in the visible spectrum, it has further been found that their spectral sensitivity can be extended into the visible part of the spectrum by the addition to the layers of sensitizers, preferably in the proportion one to three percent weight for weight of photoconductive substance. The most suitable sensitizers are dyestutf coml0 pounds, a number of which are given by way of example in the following table:

Dyestufi Group Dyestufi Compound Brilliant Green N0. 760 (p.314). Victoria Blue 13.. N o. 822 p 3-17) Trlarylmethane dyes Methyl Violet No. 783 p. 327). Crystal Violet N o. 785 (p. 329). Acid Violet 6B N0. 831 (p. 351). Xanthene dyes:

Rhodamlne B No. 864 (p. 365). Rhodamine 6G No. 866 (p. 366). Rhodamines Rhodamine G extra.-- No. 865 (p. 366). Sulphorhodamine B... No. 863 (p. 364). True acid Eosin G...- No. 870 (p. 368). Eosin S... No. 883 (p. 375). tha 13" lit 2* 23%) r ros o. p Phthalems Phloxin--- No. 2490 (p.378). Rose Bengal- N o. 889 (p. 378).

Fluorescein N0. 880 (p 373 Thiazine dyes 906 (p. 386): 924 (p. 396). 927 (p. 397).

. 1,141 (p. 499). 1,145 (p. 502). .1,148 (p. 504). .921 (p. 394).

Acridine dyes Quinoline dyes Quinone dyestuffs Anthraquinone dyestuffs Cyanine dyes Cyaniue The layer-carrying supports may be utilized for the production of images by electrophotographic means, for.

example, as follows: When the photoconductive layer has been charged, by means of, for example, a corona discharge with a charging apparatus maintained at 6000 volts, the thus sensitized layer is exposed to light under a master or by episcopic or diascopic projection and is then dusted overin known manner with a suitable developing agent such as a resin powder colored with carbon black. The resin developer is preferably obtained by fusing 30 parts by weight of polystyrene (K-Wert 55) 30 parts by weight of a maleic acid resin modified with rosin and sold under the registered trademark Beckacite K105, and 3 parts by weight of carbon black, and subsequently finely grinding the fused mass. The image that now becomes visible can easily be wiped off, and therefore needs to be fixed; it can, for example, be heated briefly to'approximately C. by means of an infra-red radiator. The temperature need not be as high as this if the heat treatment is carried out in the presence of vapors of solvents such as trichloroethylene, carbon tetrachloride or ethyl alcohol. The powdered image can also be fixed by means of steam. From positive masters, positive images of good contrast are produced.

After being fixed these electrophotographic images can be converted into printing plates: the support, e.g., the paper or plastic foil, is wiped over with a solvent for the photoconductive layer, e.g., ethyl alcohol, or acetic acid and then rinsed with water and rubbed in with greasy ink in known manner. In this way positive printing plates are obtained which can be set up in an offset machine and used for printing. They give very long runs.

If transparent supports are used the electro-phitographic images can also be used as masters for the production of further copies on any sort of light-sensitive sheets. In this respect the photoconductive compounds to be used, as provided by the invention, are superior to substances used hitherto, such as selenium or zinc oxide, inasmuch as the latter give cloudy layers because solid solutions cannot be produced with such materials and only suspensions are possible.

Where translucent supports are used for photoconductive layers, such as are provided by the invention, reflex images can also be produced. The possibility of a reflex .copy is also an advantage over the known art.

' Moreover the photoconductive layers. prepared as provided in the invention have a further important advantage in that they can be charged positively as well as negatively.

Methylene blue.. No. 1,038 (p. 449).

With positive charging the images are particularly good while there is negligible evolution of ozone, which is very considerable with negative-charging.

The invention is further illustrated in the following specific examples:

' Example 1 1 g. of the compound corresponding to Formula 28 and 1.5 g. of rosin-modified maleic acid resin, (e.g., the resin marketed by Reichhold-Chemie AG, Hamburg under the registered trademark Beckacite K 105), are dissolved in 50 cc. of a 1:1 benzeneacetone mixture. Approximately 15 cc. of this solution are distributed evenly over a paper foil (format DIN A 4). After evaporation of the solvent mixture a coating is left that adheres firmly to the surface of the paper foil. After the coating has been electrically charged and then exposed under a master by thecontact processor by diascopic or episcopic projection, an image of the master is obtained by dusting over with the resin powder colored with carbon black and subsequent heating in known manner.

, Example 2 1 g. of the compound corresponding to Formula 6 and 2 g. of rosin-modified maleic acid resin, (e.g., the resin employed in Example 1), are dissolved in a mixture of 25 cc. of acetone and 25 cc. of benzene. Two 10-00. portions of this solution are applied one after the other to a foil of transparent paper (75 g.s.m.) format DIN A 4 to form a coating. After evaporation of the solvent the dry coating, which is of yellow'color, adheres firmly to the surface of the transparent paper. In the electro-photographic process images are produced on this coating which are characterized by excellent contrast on a yellow background and can be used as masters for reproduction purposes.

Example 3 1 g. of the compound corresponding to Formula 28 and 2 g. of rosin-modified maleic acid resin, (e.g., the product marketed by Reichhold-Chernie AG, Hamburg, under the registered trademark Beckacite K 125), are dissolved in 50 cc. of a benzene/ acetone mixture in proportion of 1:1. Three l-cc. portions of this solution are applied one after the other to 2? foil of transparent paper (80 g.s.m.) of format DIN A 4 to form a coating. After evaporation of the solvent the coating is dried under an infra-red radiator; it adheres firmly to the surface of the paper foil. By electro-photographic means, images can be produced on this coating which are of good contrast with a practically colorless background and are suitable for use as masters for reproduction purposes.

Example 4 1 g. of the compound corresponding to Formula 4 and 1 g. of unsaponified ketone-aldehydecondensation-resin, e.g., the product marketed by Chemische Werke Hills AG, Marl (Krs. Reckling-hausen under the trade name Kunstharz AP), are dissolved in 30 g. of glycol monomethyl ether. The solution is applied to paper and dried. Images can be produced on this paper electrophotographically by charging the coating by means of a corona discharge and then exposing the paper beneath a positive master, followed by dusting over with the resin powder colored with carbon black in known manner. Positive images are produced that can be fixed by heat treatment with steam.

Example 5 1 g; of the compound corresponding to Formula 1, l g. of ketone resin (e.g., the ketone resin produced by the Chemische Werke Hiils AG, Marl (Kr. Recklinghausen) and marketed under the trade nameKunstharz SK), and

0.01 g. of rhodarnine B are dissolved in 30 g. of glycol monomethyl ether, and the solution applied to paper and dried. After the coating has been charged by means of a corona discharge, the sensitized paper is exposed be- 1.2 neath a positive master, for example, using a ltlO-watt incandescent lamp at a distance of approximately 15 cm. for one second. The exposed surface is then dusted over with the resin powder colored with carbon black. A positive image is produced that is fixed by treatment with trichloroethylene vapor.

Example 6 1 g. of the compound corresponding to Formula 29 and l g. of ketone resin (e.g., the resin known as Kunstharz EM produced by polycondensation by Rheinpreussen G.m.b.H., I-Iomberg (Ndrh)), are dissolved in 30 cc. of glycol monomethyl ether at C. This solution is applied to a paper foil which has been pro-coated to render it impervious to organic solvent. After evaporation of the solvent the coating adheres firmly to the surface of the paper foil. The coated foil is provided with a positive electrostatic charge in manner known per se and then exposed beneath a master, or the image of a master is projected episcopically thereon. Electrophotographic images with very good contrast on a yellow background are thereby produced on the foil.

Example 7 1 g. of the compound corresponding to Formula 30 and 1.5 g. of cournarone resin (e.g., the resin known as Cumaronharz 701/70 marketed by the Gesellschaft fiir Teerverwertung, Duisburg-Meiderich), are dissolved in a mixture of 25 cc. of benzene and 25 cc. of acetone. This solution is applied to an aluminum foil of which the surface has been previously cleaned of grease. After the solvent has evaporated and the coating has been dried the latter adheres firmly to the surface.

On this aluminum foil direct images are produced by the electrophotographic process as follows: The foil is given a positive electric charge by means of a corona discharge; it is then exposed beneath a positive master to the light of a high-pressure mercury lamp and dusted over with the resin powder colored with carbon black. The finely divided resin-carbon black mixture adheres to the parts of the coating not struck by light during exposure and a positive image becomes visible, which is stabilized (fixed) by heating slightly.

Example 8 1 g. of the compound corresponding to Formula 33 and 1 g. of zinc-modified resin (e.g. the product marketed by R. Kramer, Bremen, under the trade name Erkazit Zinkharz are dissolved in 30 cc. of benzene. The solution is applied to a paper foil prepared in accordance with American Patents 2,534,650, 2,681,617, or 2,559,- 610, or to an aluminum foil of which the surface has been cleaned of grease. After evaporation of the solvent, the coating adheres firmly to the surface of the aluminum foil. In the electrophotographic process, images with good contrast are produced on the coated foil; they are fixed by heating and then converted into a printing plate as follows: the paper or aluminum foil is wiped over with 96% ethyl alcohol, rinsed with water and rubbed in with 1% phosphoric acid and greasy ink. Positive printing plates are obtained which can be set up in an offset machine and used for printing.

Example 9 The procedure as in Example 1 is followed except that the coating solution used consists of 1 g. of the compound corresponding to Formula 4 and 1 g. of the compound corresponding to Formula 2 in 30 g. of glycol monomethyl ether. Positive images are obtained.

Example 10 13 coated paper foil is subjected to the further procedure as described in Example 1. From a positive master a positive image with very rich contrast is obtained.

Example 11 1 g. of the compound corresponding to Formula 33 and 1 g. of 2,5-bis-[4'-diethyl-aminophenyl-(1)]-l,3,4- triazole are dissolved in 30 g. of glycol monomethyl ether and the solution is applied 'to an aluminum foil. After evaporation of the solvent, the coating adheres firmly to the aluminum surface. With the coated aluminum foil so prepared, electrophotographic images can be produced as described in Example 1. If a sheet of paper is placed on the unfixed image in the carbon blackresin powder and recharging by means of a corona discharge is carried out, the said image in carbon blackresin powder is transferred from the aluminum foil to the paper to produce a mirror-image. If the cabon blackresin image is transferred to transparent paper or to a transparent plastic foil, the image obtained can be further copied, for example, on diazo photoprinting paper.

What is claimed is: 1

1. A photographic reproduction process which comprises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master to discharge the layer at the exposed portions and developing the resulting image with an electroscopic material, the photoconductive layer comprising a compound having the formula in which R'is selected from the group consisting of an aryl group and heterocyclic, aroyl, cyano, and carbalkoxy radicals, R is selected from the group consisting of hydrogen and cyano radicals, and R is selected from the group consisting of an aryl group and heterocyclic radicals.

2. A process according to claim 1 in which the photoconductive layer contains a dyestuif sensitizer.

3. A process according to claim 1 in which the photoconductive layer contains an organic colloid.

4. A photographic reproduction process which comprises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master to discharge the layer at the exposed portions and developing the resulting image with an electroscopic material, the photoconductive layer comprising a compound having the formula in which R and R are aryl groups.

5. A photographic reproduction process which comprises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master to discharge the layer at the exposed portions and developing the resulting image with an electroscopic -material, the photoconductive layer comprising a compound having the formula 14 in which R is a heterocyclic radical and R isfan aryl group.

7. A photographic reproduction process which comprises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master to discharge the layer at the exposed portions and developing the resulting image with an electroscopic material, the photoconductive layer comprising a compound having the formula ON R=N-Rr in which R and R are aryl groups.

8. A photographic reproduction process which comprises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master to discharge the layer at the exposed portions and developing the resulting image with an electroscopic material, the photoconductive layer comprising a compound having the formula :E I n 12. A process according to claim 11 in which the photoconductive layer contains a dyestufi sensitizer.

13. A process according to claim 11 in which the photoconductive layer contains an organic colloid.

14. A photographic reproduction process which comprises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master to discharge the layer at the exposed portions and developing the resulting image with an electroscopic material, the photoconductive layer comprising a, compound having the formula 15. A process according to claim 14 in which the photoconductive layer contains a dyestufi sensitizer.

16. A process according to claim 14 in which the photoconductive layer contains an organic colloid.

18. A process according to claim 17 in which the photoconductive layer contains a dyestutf sensitizer.

19. A process according to claim 17 in which the photoconductve layer contains an organic colloid.

20. A photographic reproduction process which com- NC CH5 NC C 3 21. A process according to claim 20 in which the photoconductive layer contains a dyestuff sensitizer.

22. A process according to claim 20 in which the photoconductive layer contains an organic colloid.

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1. A PHOTOGRAPHIC REPRODUCTION PROCESS WHICH COMPRISES EXPOSING AN ELECTROSTATICALLY CHARGED, SUPPORTED PHOTOCONDUCTIVE INSULATING LAYER TO LIGHT UNDER A MASTER TO DISCHARGE THE LAYER AT THE EXPOSED PORTIONS AND DEVELOPING THE RESULTING IMAGE WITH AN ELECTROSCOPIC MATERIAL, THE PHOTOCONDUCTIVE LAYER COMPRISING A COMPOUND HAVING THE FORMULA 